US 3143696 A
Description (OCR text may contain errors)
R. s. HARRIS 3,143,696 STALLED MOTOR THERMAL STOPPING CONTROL WITH PREPARATION FOR REVERSE Filed May 2, 1961 2 Sheets-Sheet 1 FIG. 1.
Aug. 4, 1 964 s, HARRIS 3,143,696
STALLED MOTOR THERMAL STOPPING CONTROL WITH PREPARATION FOR REVERSE Filed May 2, 1961 2 Sheets-Sheet 2 United at s Patfl )0.
. 3,143,696 l a STALLED MOTOR THERMAL STOPPING. CON- TROL WITH PREBARATION FOR REVERSE V 1 Roys ton'Sydney Harris, Shepherds Bush, London, Eng land, assignor to ,S. Smith & Sons (England) Limited, London, England, a British company Filed May 2, 1961, Ser. No. 197,167 Claims priority, application Great Britain May 10 Claims. (Cl. 318--266) The present invention relates to electrical actuating apparatus of the kind in which a member is moved by an electric motor through a range determined by at least one stop which mechanically prevents motion of the member beyond the range.- It is thus,.for example, appllcable to electrically actuated extendible and retractable radio aerials whose extension and/ or retraction are limited'by one. or more stops such as are frequently used onmotor vehicles. a
It is an object of the present invention to provide an electrical actuating device of the kind referred to which does not entail the use of a limit switch or the'like, mechanically operated when'the stop is reached.
According to the present invention electrical actuating apparatus comprises an electric motor, a member movable by the motor through a range determined by stop means which mechanically prevent motion of the member beyond the range, current responsive means, connecting means connecting the current responsive means in series with the motor during energisation of the motor, and contact means controlled by the current responsive means to de-energise the motor .upon persistent excess of the motor current above some'predetermined' value intermediate between that drawn by themotor when running normally and when stalled. Y j The predetermined value of current is greater than that drawn by the motor under normal runningconditions, but is less than that drawn by -the motor when it is stalled.- Thuswhen the-motor is energised to drive the member towards the stop the contact meansremain closed until the stop is reached. However, when the stop is reached, the-persistent overload current of the motor causes the contact means to be opened and the motor to be dew.
. Preferably. the current responsive meanscomprisea bimetal element actuating a normally closed contact in series with it, the element being responsive to'heat' generated in it and opening the contact when the sustainedcurrent passing through it exceeds'the said predetermined value.
Preferably the contact means and the motor are arranged'so that after de-energisation of the motor the next energisation is in the opposite sense whereby'the direction of rotation of the motor is reversed.
. The relevant features of an electrical actuating appa-' ratus for an aerial associated with a vehicle radio set will now be described with reference to the accompanying drawingsjofwhich Y i FIGURE 1 is. a schematic'representationjof the apparatus, aerial and radio set, and
I FIGURES 2 to"4show 1eaves'10,'11 and 12am plate leaf 11 may engage either contact 20 on leaf 10 or con r 3,143,696 Patented Apg. ,4, 19641 ture 5 which pivoted at 6 and held away from coil 4.
and against a stop 7 by a spring 8. Armature 5 carries an insulator block 9 which in turn carries three spring leaves 10, 11, 12 one above the other. The leaves carry contacts 20, 21, 22 positioned so that the contact 21 on '7 tact 22 on leaf 12 if leaf 11 is appropriately displaced.
A further relay coil 13 acts on an armature 14 which is pivoted at 15. Armature'14 is held against a stop 16 and away from coil 13 by a leaf spring 17. A catch.
. plate 18 (see FIGURES 2-4) of insulating material with 19 as seen in FIGURE 3.
" plate 18 is held clear of leaf 11.
. its slot 19 (FIGURE 3). -De-energisation of coil 4 now permits armature 5 to return to its original position under sation of coil 13 followed by its de-energisation permits clear of catch plate 18, opening contacts Assuming that coil 13 is de-energised and the leaf 11 lies upon the upper edge of plate 18, if coil 4 is also de-energised leaf '11 is not displaced and contact 21' does not engage either contact 20 or Contact 22. If coil 4 isenergised, armature 5 rotates about pivot 6 against the action of spring 8, causing leaf 11 to be displaced as a result of its engagement'with the plate 18. Contact 21 then engages contact 22 (FIGURE 2).
and 22. If -coil' 13 is now de-energised, catch plate 18 returns to itsoriginal position with leaf 11 lying within the action of spring 8, and leaf 11'is consequently displaced downwards with respect to leaves 10 and 12, so-
that contacts 20 and 21 engage (FIGURE 4). Energileaf 11 to spring 20 and 21. a
A contact 23 operated by a snap action bimetallic element, indicated at 24, is arranged so that currents passing through the contact'when closed also pass through the trically to radio set 1 as indicated 'at 28.
terminals 30, 31 and '32, terminal 31 normally being bimetallic element 24thereby heating it. Contact 23 is closed when element 24 is cold, and .open when the' element is at a higher temperature as a result of the sustained passage of a relatively high current. The element 24 and contact 23 are wired in parallel with coil 13. One' terminal of relay'coil 13 is connected to leaf 11 and the other terminal to the negative terminalof battery 2.
An electric motor indicated at 35 drives a winding drum 26 for a retractable aerial indicated at 27 suitable for mounting on a vehicle. The aerial is connected elec- Motor 35 has earthed- The motor winding is such that when terminal 30 1s energised drum 26 is rotated in such a direction as to extend aerial 27, and when terminal 32 is energiseddrum 26 is rotated in a direction 'to retract the aerial.-
Stops, indicated diagrammatically 'at 33, 34, limit ro t'ation of the motor appropriately inthe extending and-in" retracting direct ons. Terminal 30 is connectedto leaf 12- and terminal 32 to leaf 10.
The operation of the apparatus will now be described.
However, the parts Switch 3 is closed to energise the set 1. this causes coil :4 to be energised and since will initially be in the condition shown in FIGURE 1, leaf 11 will be displaced towards leaf 12 causing contacts 21 and 22 to engage as shown in FIGURE 2. Motor 35 is then energised in a sense to extend aerial 27. The motor current passes through coil 13 in parallel with contact 23 and element 24; but during rotation of the motor, the current drawn by the motor is not suflicient to cause either the relay 13-14 or the bimetallic If coil 13 is now energised, catch plate 18 is moved clear of leaf 11' permitting the leaf to return to a central position with respect to leaves 10 and 12, thereby opening contacts 21 .3 element'24 to operate. hen aerial 27 is fully extended stops 33, 34 engage one another, causing motor 35 to stall. The increased current heats element 24 causing it to open .contact 23with a snap action.. The current through coil 13 is'then increased to an extent sufiicient to operate the relay 13-14, moving plate 18 out of engagement with leaf 11. Contacts 21 and 22 then open, de-energising both the motor and coil 13 therebypermitting plate 18 to return to its normal position, but with leaf 11 within the slot as shown in FIGURE 3. Contact 23 re-closes as element 24 cools. I
On switching off the set by means of switch 3, coil 4 is de-energised. Armature now moves upwards displacing leaf 11 towards the leaf as shown in FIG- URE 4, contacts and 21 engage, and motor 35 is energised in a sense to retract aerial 27. When the aerial is fully retracted stops 33, 34 again engage one another, and the motor again stalls. The increased current once again causes element 24 to be displaced, opening contact 23. The increased current through coil 13 causes plate 18 tobe displaced permitting leaf 11 to return to a central position, thereby opening contacts 20, 21. Motor 35 is now de-energised as is also coil 13. Element 24 returns to its original position closing contact 23. The parts are now once again in the posi: tions shown in FIGURE 1 and ready for a fresh cycle of operations.
It will be appreciated that with the arrangement described it is not necessary for radio set 1 to be modified in any way. However, if the voltage drop produced by coil 4 is found in a particular case to detract from the performance of the set, then it is possible to wire the coil in parallel with the set instead of in series so that the working of the set is not affected. This change will however entail some small modification to the wiring of the radio set.
' While there have been described above what are presently believed to be the preferred forms of the invention, variations thereof will be obvious to those skilled in the art and all such changes and variations which fall within the spirit ofcthe invention are intended to be covered by the generic terms in the appended claims,-
which are variably worded to that end.
I claim: a 1
1. Electrical actuating apparatus comprising a reversible electric motor, a member drivable by said motor through a range determined by stop means which mechanically prevent motion of the member beyond the range thereby to stall said motor, current responsive means comprising a bi-metal element connected in series with said motor through normally closed contact means for energizing said motor, said bi-metal element being responsive to heat generated in it for opening said contact means when the current passing through it reaches a sustained value resulting from the stalling of said motor, whereby when said motor is stalled and the current drawn by said motor reaches said sustained value said current responsive means causes said contact means to de-energize the motor and causes said contact means to be set so that upon subsequent actuation the motor is energized in the opposite sense.
2. Apparatus as claimed in claim 1 wherein said concurrent responsive means and the outer ones to the motor, the middle contact being caused to engage one or other of the outer ones to energize the motor in one or other sense.
3. Apparatus as claimed in claim 2, first relay means comprising said contact means and adapted to be connected to a radio set so as to be energized when the set is energized, the contacts being acted on by the relay so that they tend to move in one direction when the relay is energized and in the opposite direction when the relay is de-energized.
4. Apparatus as claimed in claim 3, second relay means connected in parallel with the bi-metal element and its contact so as to be energized when the current through the element reaches the said sustained value member comprises an extendable vehicle aerial cooperating with a winding drum driven by the motor.
6. Apparatus as claimed in claim 1 wherein the said member comprises an extendable vehicle aerial cooperating with a winding drum driven by the motor.
7. An electrical actuating apparatus comprising an electric'motor rotatable in either of two opposing directions in dependence upon the sense in which said motor is energized, stop means for mechanically preventing rotary motion of said motor beyond the ends of a predetermined range and for stalling said motor when said ends are reached, contact means for controlling the energization of said motor, said contact means being settable to energize said motor in a sense dependent'upon the setting of said contact means, and
means responsive to the current drawn by said motor, said last-named means being connected in series with said motor and acting on said contact means when said current reaches a value indicating that said motor is stalled for causing the contact means to de-energize said motor and for causing said contact means to be reset so that upon subsequent actuation the motor is energized in an opposite sense to rotate away from one of said ends toward the other end of said range.
' 8. The apparatus of claim 7 wherein said motor current'responsive means comprises a slow-acting, bi-metal element.
9..Ihe apparatus of claim 7 wherein said contact means comprises a plurality of contacts forming part of a relay, means for setting said contacts in one direction when said relay is energized and for setting said contacts in a different direction when said relay is de-energized, and switch means for controlling the energization of said'relay;
10. The apparatus of claim 7 wherein said motor current responsive means comprises a bi-metal element actuating a switch in series therewith to open said switch when said bi-metal element deflects, and a solenoid having an energization circuit coupled to said switch, said solenoid including'a movable element for varying the setting of said contact means with variations in the deflection of said bi-metal element.
References Cited in the file of this patent 1 UNITED STATES PATENTS 2,299,785 Barrett Oct. 27, 1942 2,418,235 Menzies. Apr. 1, 1947 2,881,378 Russell Apr. 7, 1959 2,949,608 Fischer Aug. 16, 1960